docs: def expand_python_version(version):
      """
      Expand Python versions to all identifiers used on PyPI.
  
      >>> expand_python_version('3.5')
      ['3.5', 'py3', 'py2.py3', 'cp35']
      """
      if not re.match(r"^\d\.\d$", version):
          return [version]
  
      major, minor = version.split(".")
      patterns = [
          "{major}.{minor}",
          "cp{major}{minor}",
          "py{major}",
          "py{major}.{minor}",
          "py{major}{minor}",
          "source",
          "py2.py3",
      ]
      return set(pattern.format(major=major, minor=minor) for pattern in patterns)